Zoom lens

ABSTRACT

A zoom lens includes a first and a second lens group respectively having negative and positive refractive power, and changes a focal length by changing a distance between the first and the second lens group. The second lens group includes a first lens having positive refractive power and a convex surface, a second lens having positive refractive power, an aspheric surface, and a convex surface, a third lens having negative refractive power, a fourth lens having positive refractive power, and a fifth lens including one lens or more having positive refractive power. The third and the fourth lenses are connected, and the zoom lens satisfies Nd 21 &gt;1.8 and νd 24 &gt;80, where Nd 21  is a refractive index of the first lens of the second lens group at a d-line, and νd 24  is an Abbe number of the fourth lens of the second lens group at a d-line.

BACKGROUND OF THE INVENTION

This application claims priority from Japanese Patent Application No.2007-053275 filed Mar. 2, 2007, which is incorporated herein byreference in its entirety.

1. Field of the Invention

The present invention relates to a technology of a zoom lens.

2. Description of the Related Art

Recently, various electronic imaging devices such as digital stillcameras, video cameras, and surveillance camera have become common. Mostof the electronic imaging devices include a zoom lens as an imaginglens. With the miniaturization of recent electronic imaging devices,further miniaturization of the zoom lens has been demanded, and manycompact and wide-angle zoom lenses have been suggested to meet thedemand (see Japanese Patent No. 3600870 and Japanese Patent ApplicationLaid-open Publication Nos. 2006-119574 and 2002-277737).

A wide-angle zoom lens that has a large aperture and can monitor a darkplace over a wider range has been preferable for a lens of thesurveillance camera. However, due to the advance of megapixel resolutionof imaging sensors such as a charge coupled device (CCD) and acomplementary metal oxide semiconductor (CMOS), a megapixel-compatiblelens for capturing finer characteristics of a subject has been expected,and a zoom lens adaptable to the megapixel resolution of the imagingsensors has been provided (see homepage of CBC Co., Ltd., URL:

-   http://www.computar.jp/cbc_program/OUT_FILEUPLOAD_B/49.pdf)

The megapixel-compatible lens for the electronic imaging devices mustcorrect well various aberrations occurring around a screen in order tocapture finer characteristics of a subject.

However, the zoom lenses disclosed in the above three Japanese patentdocuments are unsuitable for the megapixel-compatible lens in theelectronic imaging devices since sufficient correction the aberrations,such as axial chromatic and spherical aberrations, is difficult.

Further, although the lens disclosed in the above homepage of CBC Co.,Ltd. is megapixel-compatible, the angle of view at the wide-angle endthereof is only 76°. Therefore, when a surveillance camera employing thelens disclosed in the above homepage of CBC Co., Ltd. is set at a cornerof a room, there are blind spots due to the narrow angle of view,necessitating more than two cameras to eliminate the blind spots.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least solve the aboveproblems in the conventional technologies.

A zoom lens according to an aspect of the present invention includes afirst lens group having negative refractive power and a second lensgroup having positive refractive power that are sequentially arrangedfrom a subject side, and changes a focal length by changing a distancebetween the first lens group and the second lens group. The second lensgroup includes, sequentially arranged from the subject side, a firstlens that has positive refractive power and a convex surface facingtoward the subject side, a second lens that has positive refractivepower, an aspheric surface, and a convex surface facing toward thesubject side, a third lens having negative refractive power, a fourthlens having positive refractive power, and a fifth lens including onelens or more having positive refractive power. The third lens and thefourth lens are connected. The zoom lens satisfies Nd₂₁>1.8 and νd₂₄>80,where Nd₂₁ is a refractive index of the first lens of the second lensgroup at a d-line, and νd₂₄ is an Abbe number of the fourth lens of thesecond lens group at a d-line.

The other objects, features, and advantages of the present invention arespecifically set forth in or will become apparent from the followingdetailed description of the invention when read in conjunction with theaccompanying drawings.

The other objects, features, and advantages of the present invention arespecifically set forth in or will become apparent from the followingdetailed description of the invention when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a zoom lens according to a firstexample;

FIG. 2 is a schematic illustrating various aberrations of the zoom lensaccording to the first example;

FIG. 3 is a cross sectional view of a zoom lens according to a secondexample;

FIG. 4 is a schematic illustrating various aberrations of the zoom lensaccording to the second example;

FIG. 5 is a cross sectional view of a zoom lens according to a thirdexample;

FIG. 6 is a schematic illustrating various aberrations of the zoom lensaccording to the third example;

FIG. 7 is a cross sectional view of a zoom lens according to a fourthexample;

FIG. 8 is a schematic illustrating various aberrations of the zoom lensaccording to the fourth example;

FIG. 9 is a cross sectional view of a zoom lens according to a fifthexample; and

FIG. 10 is a schematic illustrating various aberrations of the zoom lensaccording to the fifth example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the accompanying drawings, exemplary embodiments accordingto the present invention are explained in detail below.

A zoom lens according to an embodiment includes a first lens grouphaving negative refractive power and a second lens group having positiverefractive power that are sequentially arranged from a subject side. Thezoom lens changes a focal length by changing the distance between thefirst and the second lens groups.

The first lens group includes a first and a second lens that aremeniscus lenses having negative refractive power, a third lens that is abiconcave lens having negative refractive power, a fourth lens havingpositive refractive power, and a fifth lens having positive refractivepower. The first to the fifth lenses are sequentially arranged from thesubject side. The third and the fourth lenses are connected. The fifthlens may include two or more lenses.

The second lens group includes a first and a second lens thatrespectively have convex surfaces facing toward the subject side andpositive refractive power, a third lens having negative refractivepower, a fourth lens having positive refractive power, and a fifth lenshaving positive refractive power. The second lens has an asphericsurface. The third and the fourth lenses are connected. The fifth lensmay include two or more lenses.

It is an object of the present invention to provide a zoom lens havinghigh optical performance adaptable to imaging sensors having megapixelresolution. To achieve the object, sufficient correction of variousaberrations occurring around a screen is required and to meet thisrequirement, various conditions are set as follows.

Since the zoom lens according to the embodiment is a wide-angle lenshaving a large aperture and the first lens group has negative refractivepower, a beam of light emitted from the first lens group enters thesecond lens group at a very high position thereof, causing theaberrations such as spherical and coma aberrations.

Therefore, it is preferable for the zoom lens to satisfy the followingcondition where Nd₂₁ is the refractive index of the first lens of thesecond lens group at a d-line.Nd₂₁>1.8   (1)

By satisfying the condition (1), the beam emitted from the first lens ofthe second lens group can be converged, and the position at which thebeam enters the lenses subsequent to the first lens can be low.Furthermore, since the second lens of the second lens group has anaspheric surface as explained above, spherical and coma aberrations canbe effectively prevented. Moreover, since the position at which the beamenters the lenses subsequent to the first lens can be low, spherical andcoma aberrations for the lenses subsequent to the second lens can beprevented.

Furthermore, it is preferable for the zoom lens to satisfy the followingcondition where νd₂₄ is the Abbe number of the fourth lens of the secondlens group at a d-line.νd₂₄>80   (2)By satisfying the condition (2), axial chromatic aberration andchromatic aberration of magnification can be reduced due to the synergiceffect of the connection of the third and the fourth lenses of thesecond lens group.

Furthermore, by forming an aspheric surface on the subject side of thefifth lens of the second lens group, the spherical and the comaaberrations can be effectively prevented. Furthermore, by forming anaspheric surface on at least one side of the first lens of the secondlens group, the various aberrations can be prevented more effectively.

Furthermore, by making the concave surface at the connection of thethird and the fourth lenses of the second lens group face toward animage surface side, the axial chromatic aberration and the chromaticaberration of magnification can be reduced, and distortion andastigmatism can be prevented.

Furthermore, it is preferable for the zoom lens to satisfy the followingconditions where Nd₁₁, Nd₁₃, and Nd₁₄ are respectively refractiveindexes of the first, the third, and the fourth lenses of the first lensgroup at d-lines.Nd₁₁>1.7   (3)Nd₁₃>1.7   (4)Nd₁₄>1.7   (5)By satisfying the conditions (3) to (5), the coma aberration, thedistortion and the astigmatism can be prevented.

Furthermore, it is preferable for the zoom lens to satisfy the followingcondition where νd₁₃ and νd₁₄ are respectively the Abbe number of thethird and the fourth lenses of the first lens group.νd₁₃>νd₁₄   (6)By satisfying the condition (6), the chromatic aberration ofmagnification can be reduced due to the synergic effect of theconnection of the third and the fourth lenses of the first lens group.

Furthermore, since the fifth lens having the positive refractive powerof the first lens group is arranged closest to the image surface, thecoma and the spherical aberrations can be prevented.

As explained above, since the zoom lens according to the embodiment hasthe above characteristics, the zoom lens is wide-angled, has a largeaperture, high optical performance, and is adaptable to the imagesensors having megapixel resolution. Furthermore, since the zoom lensincludes the lens having the aspheric surface, the various aberrationscan be effectively corrected with fewer lenses, and a reduction in size,weight, and manufacturing cost can be achieved.

When the values of the parameters are respectively close to thethresholds shown in the conditions (1) to (5), the effect of the presentinvention can be achieved.

Examples of the zoom lens according to the present invention areexplained below.

FIG. 1 is a cross sectional view of a zoom lens according to a firstexample. A zoom lens 100 includes a first lens group G₁₁ having negativerefractive power and a second lens group G₁₂ having positive refractivepower that are sequentially arranged from a subject side (not shown).The zoom lens 100 changes a focal length by changing the distancebetween the first lens group G₁₁ and the second lens group G₁₂. Anaperture stop (STP) is arranged between the first lens group G₁₁ and thesecond lens group G₁₂.

The first lens group G₁₁ includes a first lens L₁₁₁ that is a meniscuslens having negative refractive power, a second lens L₁₁₂ that is ameniscus lens having negative refractive power, a third lens L₁₁₃ thatis a biconcave lens having negative refractive power, a fourth lens L₁₁₄having positive refractive power, and a fifth lens L₁₁₅ having positiverefractive power. The first to the fifth lenses are sequentiallyarranged from the subject side. The third lens L₁₁₃ and the fourth lensL₁₁₄ are connected.

The second lens group G₁₂ includes a first lens L₁₂₁ that has positiverefractive power and a convex surface facing toward the subject side, asecond lens L₁₂₂ that has positive refractive power and a convex surfacefacing toward the subject side, a third lens L₁₂₃ having negativerefractive power, a fourth lens L₁₂₄ having positive refractive power,and a fifth lens L₁₂₅ having positive refractive power. The first to thefifth lenses are sequentially arranged from the subject side. Asphericsurfaces are formed on both sides of the second lens L₁₂₂. The thirdlens L₁₂₃ and the fourth lens L₁₂₄ are connected, and a concave surfaceat the connection faces toward an image surface side. Aspheric surfacesare formed on both sides of the fifth lens L₁₂₅.

Various data of the zoom lens according to the first example is shownbelow.

-   Focal length (f)=3.09˜7.80 mm-   F number=1.0 (wide-angle end)˜1.6 (telephoto end)-   Angle of view (2ω)=118° (wide-angle end)˜44° (telephoto end)-   Refractive index of the first lens L₁₂₁ of the second lens group G₁₂    at the d-line concerning the condition (1) (Nd₂₁)=1.83481-   Abbe number of the fourth lens L₁₂₄ of the second lens group G₁₂ at    the d-line concerning the condition (2) (νd₂₄)=81.6-   Refractive index of the first lens L₁₁₁ of the first lens group G₁₁    at the d-line concerning the condition (3) (Nd₁₁)=1.83481-   Refractive index of the third lens L₁₁₃ of the first lens group G₁₁    at the d-line concerning the condition (4) (Nd₁₃)=1.77250-   Refractive index of the fourth lens L₁₁₄ of the first lens group G₁₁    at the d-line concerning the condition (5) (Nd₁₄)=1.84666-   Abbe number of the third lens L₁₁₃ of the first lens group G₁₁ at    the d-line concerning the condition (6) (νd₁₃)=49.6-   Abbe number of the fourth lens L₁₁₄ of the first lens group G₁₁ at    the d-line concerning the condition (6) (νd₁₄)=23.8-   r₁=60. 6033    -   d₁=1.2, nd₁=1.83481, νd₁=42.7-   r₂=10.8740    -   d₂=2.05-   r₃=18.7901    -   d₃=1.1, nd₂=1.77250, νd₂=49.6-   r₄=10.1709    -   d₄=3.58-   r₅=−49.6783    -   d₅=0.8, nd₃=1.77250, νd₃=49.6-   r₆=14.0473    -   d₆=2.2, nd₄=1.84666, νd₄=23.8-   r₇=24.1536    -   d₇=0.7-   r₈=21.0585    -   d₈=2.2, nd₅=1.84666, νd₅=23.8-   r₉=491.3684    -   d₉g=28.03 (wide-angle end)˜4.29 (telephoto end)-   r₁₀=14.9565    -   d₁₀=3.8, nd₆=1.83481, νd₆=42.7-   r₁₁=−357.1039    -   d₁₁=0.15-   r₁₂=14.1240 (aspheric surface)    -   d₁₂=2.6, nd₇=1.58313, νd₇=59.5-   r₁₃=46.6858 (aspheric surface)    -   d₁₃=0.7-   r₁₄=325.9099    -   d₁₄=1, nd₈=1.92286, νd₈=20.9-   r₁₅=10.2931    -   d₁₅=3.5, nd₉=1.49700, νd₉=81.6-   r₁₆=15.6119    -   d₁₆=1-   r₁₇=14.0429 (aspheric surface)    -   d₁₇=3.2, nd₁₀=1.58313, νd₁₀=59.5-   r₁₈=−13.2892 (aspheric surface)    -   d₁₈=8.13 (wide-angle end)˜14.66 (telephoto end)-   r₁₉=∞-   Cone coefficient (k) and aspheric coefficients (A, B, C, D, E)    (Twelfth Surface)-   k=8.27400×10⁻¹, A=0,-   B=−1.00359×10⁻⁴, C=−3.83431×10⁻⁷,-   D=−5.88011×10⁻⁸, E=5.12547×10⁻¹⁰    (Thirteenth Surface)-   k=8.60080, A=0,-   B=−4.76037×10⁻⁵, C=−2.72848×10⁻⁷,-   D=−3.95440×10⁻⁸, E=5.43116×10⁻¹⁰    (Seventeenth Surface)-   k=2.47570, A=0,-   B=−3.91850×10⁻⁴, C=−3.29584×10⁻⁷,-   D=−7.51468×10⁻⁹, E=3.15114×10⁻¹⁰    (Eighteenth Surface)-   k=9.08200×10⁻¹, A=0,-   B=−3.92502×10⁻⁵, C=−1.51006×10⁻⁷,-   D=−4.92045×10⁻⁹, E=2.71461×10⁻¹²

FIG. 2 is a schematic illustrating various aberrations of the zoom lensaccording to the first example. Fno and 2ω respectively indicate an Fnumber and an angle of view. g, d, and c indicate aberrationscorresponding to wavelengths of the g-line (λ=546.07 nm), the d-line(λ=587.6 nm), and the c-line (λ=656.3 nm), respectively. ΔS and ΔMrespectively indicate aberrations with respect to the sagittal and themeridional image surfaces.

FIG. 3 is a cross sectional view of a zoom lens according to a secondexample. A zoom lens 200 includes a first lens group G₂₁ having negativerefractive power and a second lens group G₂₂ having positive refractivepower that are sequentially arranged from a subject (not shown). Thezoom lens 200 changes a focal length by changing the distance betweenthe first lens group G₂₁ and the second lens group G₂₂. An STP isarranged between the first lens group G₂₁ and the second lens group G₂₂.

The first lens group G₂₁ includes a first lens L₂₁₁ that is a meniscuslens having negative refractive power, a second lens L₂₁₂ that is ameniscus lens having negative refractive power, a third lens L₂₁₃ thatis a biconcave lens having negative refractive power, a fourth lens L₂₁₄having positive refractive power, and a fifth lens L₂₁₅ having positiverefractive power. The first to the fifth lenses are sequentiallyarranged from the subject side. The third lens L₂₁₃ and the fourth lensL₂₁₄ are connected.

The second lens group G₂₂ includes a first lens L₂₂₁ that has positiverefractive power and a convex surface facing toward the subject side, asecond lens L₂₂₂ that has positive refractive power and a convex surfacefacing toward the subject side, a third lens L₂₂₃ having negativerefractive power, a fourth lens L₂₂₄ having positive refractive power,and a fifth lens L₂₂₅ that includes two lenses having positiverefractive power. The first to the fifth lenses are sequentiallyarranged from the subject side. Aspheric surfaces are formed on bothsides of the second lens L₂₂₂. The third lens L₂₂₃ and the fourth lensL₂₂₄ are connected, and a concave surface at the connection faces towardan image surface side. An aspheric surface is formed on a side of thefifth lens L₂₂₅ that is closest to the subject side.

Various data of the zoom lens according to the second example is shownbelow.

-   Focal length (f)=3.09˜7.80 mm-   F number=1.0 (wide-angle end)˜1.5 (telephoto end)-   Angle of view (2ω)=119° (wide-angle end)˜44° (telephoto end)-   Refractive index of the first lens L₂₂₁ of the second lens group G₂₂    at the d-line concerning the condition (1) (Nd₂₁)=1.83481-   Abbe number of the fourth lens L₂₂₄ of the second lens group-   G₂₂ at the d-line concerning the condition (2) (νd₂₄)=81.6-   Refractive index of the first lens L₂₁₁ of the first lens group G₂₁    at the d-line concerning the condition (3) (Nd₁₁)=1.83400-   Refractive index of the third lens L₂₁₃ of the first lens group G₂₁    at the d-line concerning the condition (4) (Nd₁₃)=1.77250-   Refractive index of the fourth lens L₂₁₄ of the first lens group G₂₁    at the d-line concerning the condition (5) (Nd₁₄)=1.84666-   Abbe number of the third lens L₂₁₃ of the first lens group G₂₁ at    the d-line concerning the condition (6) (νd₁₃)=49.6-   Abbe number of the fourth lens L₂₁₄ of the first lens group G₂₁ at    the d-line concerning the condition (6) (νd₁₄)=23.8-   r₁=55.8123    -   d₁=1.2, nd₁=1.83400, νd₁=37.2-   r₂=10.9411    -   d₂=2.05-   r₃=15.1739    -   d₃=1.1, nd₂=1.51633, νd₂=64.2-   r₄=9.0642    -   d₄=3.58-   r₅=−44.4381    -   d₅=0.8, nd₃=1.77250, νd₃=49.6-   r₆=11.4504    -   d₆=2.2, nd₄=1.84666, νd₄=23.8-   r₇=18.6833    -   d₇=0.7-   r₈=18.2720    -   d₈=2.2, nd₅=1.84666, νd₅=23.8-   r₉=150.5239    -   d₉=28.60 (wide-angle end)˜4.43 (telephoto end)-   r₁₀=16.1642    -   d₁₀=3.8, nd₆=1.83481, νd₆=42.7-   r₁₁=−99.2546    -   d₁₁=0.15-   r₁₂=12.0389 (aspheric surface)    -   d₁₂=2.6, nd₇=1.58313, νd₇=59.5-   r₁₃=33.1910 (aspheric surface)    -   d₁₃=0.7-   r₁₄=451.9460    -   d₁₄=1, nd₈=1.92286, νd₈=20.9-   r₁₅=9.6171    -   d₁₅=3.5, nd₉=1.49700, νd₉=81.6-   r₁₆=14.7193    -   d₁₆=1-   r₁₇=16.9707 (aspheric surface)    -   d₁₇=3.2, nd₁₀=1.69350, νd₁₀=53.2-   r₁₈=−35.2893    -   d₁₈=0.3-   r₁₉=142.9618    -   d₁₉=2, nd₁₁=1.77250, νd₁₁=49.6-   r₂₀=−31.6496    -   d₂₀=6.95 (wide-angle end)˜13.13 (telephoto end)-   r₂₁=∞-   Cone coefficient (k) and aspheric coefficients (A, B, C, D, E)    (Twelfth Surface)-   k=9.44000×10⁻¹, A=0,-   B=−2.13258×10⁻⁵, C=−1.39439×10⁻⁶,-   D=−4.80023×10⁻⁸, E=−1.86387×10⁻¹⁰    (Thirteenth Surface)-   k=8.95650, A=0,-   B=5.02498×10⁻⁵, C=−4.17564×10⁻⁶,-   D=−4.78727×10⁻⁸, E=4.69304×10⁻¹⁰    (Seventeenth Surface)-   k=4.91630, A=0,-   B=−2.37108×10⁻⁴, C=−1.51533×10⁻⁶,-   D=−3.67432×10⁻⁸, E=4.28340×10⁻¹⁰

FIG. 4 is a schematic illustrating various aberrations of the zoom lensaccording to the second example. Fno and 2ω respectively indicate an Fnumber and an angle of view. g, d, and c indicate aberrationscorresponding to wavelengths of the g-line (λ=546.07 nm), the d-line(λ=587.6 nm), and the c-line (λ=656.3 nm), respectively. ΔS and ΔMrespectively indicate aberrations with respect to the sagittal and themeridional image surfaces.

FIG. 5 is a cross sectional view of a zoom lens according to a thirdexample. A zoom lens 300 includes a first lens group G₃₁ having negativerefractive power and a second lens group G₃₂ having positive refractivepower that are sequentially arranged from a subject side (not shown).The zoom lens 300 changes a focal length by changing the distancebetween the first lens group G₃₁ and the second lens group G₃₂. An STPis arranged between the first lens group G₃₁ and the second lens groupG₃₂.

The first lens group G₃₁ includes a first lens L₃₁₁ that is a meniscuslens having negative refractive power, a second lens L₃₁₂ that is ameniscus lens having negative refractive power, a third lens L₃₁₃ thatis a biconcave lens having negative refractive power, a fourth lens L₃₁₄having positive refractive power, and a fifth lens L₃₁₅ having positiverefractive power. The first to the fifth lenses are sequentiallyarranged from the subject side. The third lens L₃₁₃ and the fourth lensL₃₁₄ are connected.

The second lens group G₃₂ includes a first lens L₃₂₁ that has positiverefractive power and a convex surface facing toward the subject side, asecond lens L₃₂₂ that has positive refractive power and a convex surfacefacing toward the subject side, a third lens L₃₂₃ having negativerefractive power, a fourth lens L₃₂₄ having positive refractive power,and a fifth lens L₃₂₅ having positive refractive power. The first to thefifth lenses are sequentially arranged from the subject side. Anaspheric surface is formed on the subject side of the first lens L₃₂₁.Aspheric surfaces are formed on both sides of the second lens L₃₂₂. Thethird lens L₃₂₃ and the fourth lens L₃₂₄ are connected, and a concavesurface at the connection faces toward an image surface side. Asphericsurfaces are formed on both sides of the fifth lens L₃₂₅.

Various data of the zoom lens according to the third example is shownbelow.

-   Focal length (f)=3.09˜7.80 mm-   F number=1.0 (wide-angle end)˜1.6 (telephoto end)-   Angle of view (2ω))=119° (wide-angle end)˜44° (telephoto end)-   Refractive index of the first lens L₃₂₁ of the second lens group G₃₂    at the d-line concerning the condition (1) (Nd₂₁)=1.88300-   Abbe number of the fourth lens L₃₂₄ of the second lens group G₃₂ at    the d-line concerning the condition (2) (νd₂₄)=81.6-   Refractive index of the first lens L₃₁₁ of the first lens group G₃₁    at the d-line concerning the condition (3) (Nd₁₁)=1.83481-   Refractive index of the third lens L₃₁₃ of the first lens group G₃₁    at the d-line concerning the condition (4) (Nd₁₃)=1.77250-   Refractive index of the fourth lens L₃₁₄ of the first lens group G₃₁    at the d-line concerning the condition (5) (Nd₁₄)=1.84666-   Abbe number of the third lens L₃₁₃ of the first lens group G₃₁ at    the d-line concerning the condition (6) (νd₁₃)=49.6-   Abbe number of the fourth lens L₃₁₄ of the first lens group G₃₁ at    the d-line concerning the condition (6) (νd₁₄)=23.8-   r₁=64.9127    -   d₁=1.2, nd₁=1.83481, νd₁=42.7-   r₂=10.9174    -   d₂=2.05-   r₃=18.9499    -   d₃=1.1, nd₂=1.77250, νd₂=49.6-   r₄=10.0782    -   d₄=3.5-   r₅=−49.4618    -   d₅=0.8, nd₃=1.77250, νd₃=49.6-   r₆=14.8542    -   d₆=2.2, nd₄=1.84666, νd₄=23.8-   r₇=23.6065    -   d₇=0.7-   r₈=20.7533    -   d₈=2.2, nd₅=1.84666, νd₅=23.8-   r₉=498.2260    -   d₉=27.60 (wide-angle end)˜4.33 (telephoto end)-   r₁₀=15.0799 (aspheric surface)    -   d₁₀=4.2, nd₆=1.88330, νd₆=40.8-   r₁₁=−488.0928    -   d₁₁=0.15-   r₁₂=14.2660 (aspheric surface)    -   d₁₂=2.6, nd₇=1.58313, νd₇=59.5-   r₁₃=46.0664 (aspheric surface)    -   d₁₃=0.7-   r₁₄=488.9254    -   d₁₄=1, nd₈=1.92286, νd₈=20.9-   r₁₅=9.7322    -   d₁₅=3.5, nd₉=1.49700, νd₉=81.6-   r₁₆=16.5501    -   d₁₆=1-   r₁₇=13.8353 (aspheric surface)    -   d₁₇=3.2, nd₁₀=1.58313, νd₁₀=59.5-   r₁₈=−13.5661 (aspheric surface)    -   d₁₈=7.99 (wide-angle end)˜14.70 (telephoto end)-   r₁₉=∞-   Cone coefficient (k) and aspheric coefficients (A, B, C, D, E)    (Tenth Surface)-   k=9.79300×10⁻¹, A=0,-   B=−1.15675×10⁻⁶, C=−1.3581×10⁻⁸,-   D=−1.61354×10⁻¹⁰, E=−1.34196×10⁻¹²    (Twelfth Surface)-   k=8.4470×10⁻¹, A=0,-   B=−9.97588×10⁻⁵, C=−3.55011×10⁻⁷,-   D=−5.82412×10⁻⁸, E=5.23118×10⁻¹⁰    (Thirteenth Surface)-   k=8.19940, A=0,-   B=−4.83212×10⁻⁵, C=−2.93684×10⁻⁷,-   D=−4.02161×10⁻⁸, E=5.32036×10⁻¹⁰    (Seventeenth Surface)-   k=2.51040, A=0,-   B=−3.86883×10⁻⁴, C=−3.53290×10⁻⁷,-   D=−5.27952×10⁻⁹, E=3.92750×10⁻¹⁰    (Eighteenth Surface)-   k=8.91600×10⁻¹, A=0,-   B=−3.86305×10⁻⁵, C=3.13142×10⁻⁹,-   D=−7.96596×10⁻¹⁰, E=9.16774×10⁻¹¹

FIG. 6 is a schematic illustrating various aberrations of the zoom lensaccording to the third example. Fno and 2ω respectively indicate an Fnumber and an angle of view. g, d, and c indicate aberrationscorresponding to wavelengths of the g-line (λ=546.07 nm), the d-line(λ=587.6 nm), and the c-line (λ=656.3 nm), respectively. ΔS and ΔMrespectively indicate aberrations with respect to the sagittal and themeridional image surfaces.

FIG. 7 is a cross sectional view of a zoom lens according to a fourthexample. A zoom lens 400 includes a first lens group G₄₁ having negativerefractive power and a second lens group G₄₂ having positive refractivepower that are sequentially arranged from a subject side (not shown).The zoom lens 400 changes a focal length by changing the distancebetween the first lens group G₄₁ and the second lens group G₄₂. An STPis arranged between the first lens group G₄₁ and the second lens groupG₄₂.

The first lens group G₄₁ includes a first lens L₄₁₁ that is a meniscuslens having negative refractive power, a second lens L₄₁₂ that is ameniscus lens having negative refractive power, a third lens L₄₁₃ thatis a biconcave lens having negative refractive power, a fourth lens L₄₁₄having positive refractive power, and a fifth lens L₄₁₅ having positiverefractive power. The first to the fifth lenses are sequentiallyarranged from the subject side. The third lens L₄₁₃ and the fourth lensL₄₁₄ are connected.

The second lens group G₄₂ includes a first lens L₄₂₁ that has positiverefractive power and a convex surface facing toward the subject side, asecond lens L₄₂₂ that has positive refractive power and a convex surfacefacing toward the subject side, a third lens L₄₂₃ having negativerefractive power, a fourth lens L₄₂₄ having positive refractive power,and a fifth lens L₄₂₅ having positive refractive power. The first to thefifth lenses are sequentially arranged from the subject side. Anaspheric surface is formed on an image surface side of the first lensL₄₂₁. Aspheric surfaces are formed on both sides of the second lensL₄₂₂. The third lens L₄₂₃ and the fourth lens L₄₂₄ are connected, and aconcave surface at the connection faces toward the image surface side.Aspheric surfaces are formed on both sides of the fifth lens L₄₂₅.

Various data of the zoom lens according to the fourth example is shownbelow.

-   Focal length (f)=3.09˜7.80 mm-   F number=1.0 (wide-angle end)˜1.6 (telephoto end)-   Angle of view (2ω)=119° (wide-angle end)˜44° (telephoto end)-   Refractive index of the first lens L₄₂₁ of the second lens group G₄₂    at the d-line concerning the condition (1) (Nd₂₁)=1.83481-   Abbe number of the fourth lens L₄₂₄ of the second lens group G₄₂ at    the d-line concerning the condition (2) (νd₂₄)=81.6-   Refractive index of the first lens L₄₁₁ of the first lens group G₄₁    at the d-line concerning the condition (3) (Nd₁₁)=1.83481-   Refractive index of the third lens L₄₁₃ of the first lens group G₄₁    at the d-line concerning the condition (4) (Nd₁₃)=1.77250-   Refractive index of the fourth lens L₄₁₄ of the first lens group G₄₁    at the d-line concerning the condition (5) (Nd₁₄)=1.84666-   Abbe number of the third lens L₄₁₃ of the first lens group G₄₁ at    the d-line concerning the condition (6) (νd₁₃)=49.6-   Abbe number of the fourth lens L₄₁₄ of the first lens group G₄₁ at    the d-line concerning the condition (6) (νd₁₄)=23.8-   r₁=64.9079    -   d₁=1.2, nd₁=1.83481, νd₁=42.7-   r₂=10.9922    -   d₂=2.05-   r₃=19.5773    -   d₃=1.1, nd₂=1.77250, νd₂=49.6-   r₄=10.3857    -   d₄=3.58-   r₅=−46.9958    -   d₅=0.8, nd₃=1.77250, νd₃=49.6-   r₆=19.0159    -   d₆=2.2, nd₄=1.84666, νd₄=23.8-   r₇=24.4858    -   d₇=0.7-   r₈=21.7135    -   d₈=2.5, nd₅=1.92286, νd₅=20.9-   r₉=379.1354    -   d₉=28.09 (wide-angle end)˜3.45 (telephoto end)-   r₁₀=14.8432    -   d₁₀=4, nd₆=1.83481, νd₆=42.7-   r₁₁=−422.4805 (aspheric surface)    -   d₁₁=0.15-   r₁₂=14.0188 (aspheric surface)    -   d₁₂=2.6, nd₇=1.58313, νd₇=59.5-   r₁₃=48.5354 (aspheric surface)    -   d₁₃=0.7-   r₁₄=455.5553    -   d₁₄=1, nd₈=1.92286, νd₈=20.9-   r₁₅=10.1482    -   d₁₅=3.5, nd₉=1.49700, νd₉=81.6-   r₁₆=15.9114    -   d₁₆=1-   r₁₇=13.7916 (aspheric surface)    -   d₁₇=3.2, nd₁₀=1.58313, νd₁₀=59.5-   r₁₈=−13.5985 (aspheric surface)    -   d₁₈=7.94 (wide-angle end)˜15.73 (telephoto end)-   r₁₉=∞-   Cone coefficient (k) and aspheric coefficients (A, B, C, D, E)    (Eleventh Surface)-   k=−2.95000×10², A=0,-   B=1.19722×10⁻⁶, C=3.56071×10⁻⁸,-   D=5.97730×10⁻¹⁰, E=−4.50861×10⁻¹²    (Twelfth Surface)-   k=8.75700×10⁻¹, A=0,-   B=−9.95106×10⁻⁵, C=−2.07044×10⁻⁷,-   D=−5.89465×10⁻⁸, E=5.14731×10⁻¹⁰    (Thirteenth Surface)-   k=9.35610, A=0,-   B=−4.61820×10⁻⁵, C=−3.29212×10⁻⁷,-   D=−3.94493×10⁻⁸, E=5.06525×10⁻¹⁰    (Seventeenth Surface)-   k=2.38150, A=0,-   B=−3.83180×10⁻⁴, C=−7.18720×10⁻⁷,-   D=−1.87515×10⁻⁹, E=4.3322×10⁻¹⁰    (Eighteenth Surface)-   k=8.42900×10⁻¹, A=0,-   B=−3.64406×10⁻⁵, C=1.49696×10⁻⁷,-   D=−9.79469×10⁻¹⁰, E=2.92381×10⁻¹⁰

FIG. 8 is a schematic illustrating various aberrations of the zoom lensaccording to the fourth example. Fno and 2ω respectively indicate an Fnumber and an angle of view. g, d, and c indicate aberrationscorresponding to wavelengths of the g-line (λ=546.07 nm), the d-line(λ=587.6 nm), and the c-line (λ=656.3 nm), respectively. ΔS and ΔMrespectively indicate aberrations with respect to the sagittal and themeridional image surfaces.

FIG. 9 is a cross sectional view of a zoom lens according to a fifthexample. A zoom lens 500 includes a first lens group G₅₁ having negativerefractive power and a second lens group G₅₂ having positive refractivepower that are sequentially arranged from a subject side (not shown).The zoom lens 500 changes a focal length by changing the distancebetween the first lens group G₅₁ and the second lens group G₅₂. An STPis arranged between the first lens group G₅₁ and the second lens groupG₅₂.

The first lens group G₅₁ includes a first lens L₅₁₁ that is a meniscuslens having negative refractive power, a second lens L₅₁₂ that is ameniscus lens having negative refractive power, a third lens L₅₁₃ thatis a biconcave lens having negative refractive power, a fourth lens L₅₁₄having positive refractive power, and a fifth lens L₅₁₅ that includestwo lenses having positive refractive power. The first to the fifthlenses are sequentially arranged from the subject side. The third lensL₅₁₃ and the fourth lens L₅₁₄ are connected.

The second lens group G₅₂ includes a first lens L₅₂₁ that has positiverefractive power and a convex surface facing toward the subject side, asecond lens L₅₂₂ that has positive refractive power and a convex surfacefacing toward the subject side, a third lens L₅₂₃ having negativerefractive power, a fourth lens L₅₂₄ having positive refractive power,and a fifth lens L₅₂₅ having positive refractive power. The first to thefifth lenses are sequentially arranged from the subject side. Asphericsurfaces are formed on both sides of the second lens L₅₂₂. The thirdlens L₅₂₃ and the fourth lens L₅₂₄ are connected, and a concave surfaceat the connection faces toward an image surface side. Aspheric surfacesare formed on both sides of the fourth lens L₅₂₄.

Various data of the zoom lens according to the fifth example is shownbelow.

-   Focal length (f)=3.09˜7.80 mm-   F number=1.0 (wide-angle end)˜1.5 (telephoto end)-   Angle of view (2ω)=118° (wide-angle end)˜44° (telephoto end)-   Refractive index of the first lens L₅₂₁ of the second lens group G₅₂    at the d-line concerning the condition (1) (Nd₂₁)=1.83481-   Abbe number of the fourth lens L₅₂₄ of the second lens group G₅₂ at    the d-line concerning the condition (2) (νd₂₄)=81.6-   Refractive index of the first lens L₅₁₁ of the first lens group G₅₁    at the d-line concerning the condition (3) (Nd₁₁)=1.83481-   Refractive index of the third lens L₅₁₃ of the first lens group G₅₁    at the d-line concerning the condition (4) (Nd₁₃)=1.77250-   Refractive index of the fourth lens L₅₁₄ of the first lens group G₅₁    at the d-line concerning the condition (5) (Nd₁₄)=1.84666-   Abbe number of the third lens L₅₁₃ of the first lens group G₅₁ at    the d-line concerning the condition (6) (νd₁₃)=49.6-   Abbe number of the fourth lens L₅₁₄ of the first lens group G₅₁ at    the d-line concerning the condition (6) (νd₁₄)=23.8-   r₁=60.5734    -   d₁=1.2, nd₁=1.83481, νd₁=42.7-   r₂=11.1643    -   d₂=2.06-   r₃=26.2792    -   d₃=1.1, nd₂=1.77250, νd₂=49.6-   r₄=11.1041    -   d₄=3.59-   r₅=−50.546    -   d₅=0.8, nd₃=1.77250, νd₃=49.6-   r₆=14.4653    -   d₆=2.2, nd₄=1.84666, νd₄=23.8-   r₇=23.2261    -   d₇=0.5-   r₈=42.2195    -   d₈=1.5, nd₅=1.84666, νd₅=23.8-   r₉=105.2362    -   d₉=0.2-   r₁₀=23.2419    -   d₁₀=2.2, nd₆=1.84666, νd₆=23.8-   r₁₁=131.754    -   d₁₁=26.44 (wide-angle end)˜3.19 (telephoto end)-   r₁₂=14.4618    -   d₁₂=3.8, nd₇=1.83481, νd₇=42.7-   r₁₃=−463.3355    -   d₁₃=0.15-   r₁₄=14.9229 (aspheric surface)    -   d₁₄=2.6, nd₈=1.58313, νd₈=59.5-   r₁₅=62.3666 (aspheric surface)    -   d₁₅=0.7-   r₁₆=254.2529    -   d₁₆=1, nd₉=1.92286, νd₉=20.9-   r₁₇=10.0434 (aspheric surface)    -   d₁₇=3.5, nd₁₀=1.49700, νd₁₀=81.6-   r₁₈=15.2948 (aspheric surface)    -   d₁₈=1-   r₁₉=14.4335    -   d₁₉=3.2, nd₁₁=1.58313, νd₁₁=59.5-   r₂₀=−13.4136    -   d₂₀=8.04 (wide-angel end)˜14.68 (telephoto end)-   r₂₁=∞-   Cone coefficient (k) and aspheric coefficients (A, B, C, D, E)    (Fourteenth Surface)-   k=7.30200×10⁻¹, A=0,-   B=−1.07745×10⁻⁴, C=−3.84171×10⁻⁷,-   D=−5.65524×10⁻⁸, E=5.15563×10⁻¹⁰    (Fifteenth Surface)-   k=1.56235×10, A=0,-   B=−4.11663×10⁻⁵, C=−2.26754×10⁻⁷,-   D=−3.67543×10⁻⁸, E=4.80302×10⁻¹⁰    (Seventeenth Surface)-   k=2.67600, A=0,-   B=−3.93389×10⁻⁴, C=−1.11715×10⁻⁷,-   D=−3.73849×10⁻⁸, E=1.21867×10⁻⁹    (Eighteenth Surface)-   k=9.65000×10⁻¹, A=0,-   B=−3.97337×10⁻⁵, C=−5.49935×10⁻⁷,-   D=7.11544×10⁻⁹, E=2.52492×10⁻¹⁰

FIG. 10 is a schematic illustrating various aberrations of the zoom lensaccording to the fifth example. Fno and 2ω respectively indicate an Fnumber and an angle of view. g, d, and c indicate aberrationscorresponding to wavelengths of the g-line (λ=546.07 nm), the d-line(λ=587.6 nm), and the c-line (λ=656.3 nm), respectively. ΔS and ΔMrespectively indicate aberrations with respect to the sagittal and themeridional image surfaces.

In the above data, r_(i) indicates a curvature radius of each lens,d_(i) indicates a thickness of each lens or an interval of lenssurfaces, nd_(i) indicates a refractive index of each lens at thed-line, and νd_(i) indicates an Abbe number of each lens at the d-linewhere i is a positive integer.

The each aspheric surface is expressed by the following equation.

$X = {\frac{( {1/R} )Y^{2}}{1 + \sqrt{1 - {k( {Y/R} )}^{2}}} + {A\; Y^{2}} + {B\; Y^{4}} + {C\; Y^{6}} + {D\; Y^{8}} + {E\; Y^{10}}}$

Where, X is the X-axis along an optical axis, Y is the Y-axisperpendicular to the optical axis, a travel direction of light ispositive, R is a paraxial curvature radius, and A, B, C, D, and Erespectively indicate two, four, six, eight, and ten dimensionalaspheric coefficients.

As explained above, since the zoom lens according to the embodiment hasthe above characteristics, the zoom lens becomes wide-angled, has alarge aperture, high performance, and is adaptable to imaging sensorshaving megapixel resolution. Since the angle of view at the wide-angleend is equal to or more than 100° (horizontal angle of view is equal toor more than 90°), the F number is equal to or more than approximately1.4, and the various aberrations can be well corrected, the zoom lens issuitable for the megapixel-compatible electronic imaging devices.Furthermore, since the zoom lens includes a lens having an asphericsurface, the various aberrations can be well corrected with fewerlenses, and a reduction in size, weight, and manufacturing cost can beachieved.

Thus, the zoom lens according to the embodiment described, is useful formegapixel-compatible electronic imaging devices, such as a digital stillcamera, a video camera, and a surveillance camera, and is especiallysuitable when high optical performance is needed.

Although the invention has been described with respect to a specificembodiment for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

1. A zoom lens that includes a first lens group having negativerefractive power and a second lens group having positive refractivepower that are sequentially arranged from a subject side, and changes afocal length by changing a distance between the first lens group and thesecond lens group, wherein the second lens group includes, sequentiallyarranged from the subject side, a first lens that has positiverefractive power and a convex surface facing toward the subject side, asecond lens that has positive refractive power, an aspheric surface, anda convex surface facing toward the subject side, a third lens havingnegative refractive power, a fourth lens having positive refractivepower, and a fifth lens including one lens or more having positiverefractive power, the third lens and the fourth lens are connected, andthe zoom lens satisfies following conditions,Nd₂₁>1.8νd₂₄>80 where Nd₂₁ is a refractive index of the first lens of the secondlens group at a d-line, and νd₂₄is an Abbe number of the fourth lens ofthe second lens group at a d-line.
 2. The zoom lens according to claim1, wherein a surface of the fifth lens of the second lens group that isclosest to the subject side is an aspheric surface.
 3. The zoom lensaccording to claim 1, wherein at least one surface of the first lens ofthe second lens group is an aspheric surface.
 4. The zoom lens accordingto claim 1, wherein a concave surface at a connection of the third lensand the fourth lens of the second lens group faces toward an imagesurface side.
 5. The zoom lens according to claim 1, wherein the firstlens group includes, sequentially arranged from the subject side, afirst lens and a second lens, each of which is a meniscus lens havingnegative refractive power, a third lens that is a biconcave lens havingnegative refractive power, a fourth lens having positive refractivepower, and a fifth lens that includes one lens or more having positiverefractive power, the third lens and the fourth lens are connected, andthe zoom lens satisfies following conditions,Nd₁₁>1.7Nd₁₃>1.7Nd₁₄>1.7νd₁₃>νd₁₄ where Nd₁₁, Nd₁₃, and Nd₁₄ are respectively refractive indexesof the first lens, the third lens, and the fourth lens of the first lensgroup, and νd₁₃ and νd₁₄are respectively Abbe numbers of the third lensand the fourth lens of the first lens group.